If his mane is very thick thin it and then pull
You can get a pulling blade comb from horseland but I think it buy pull there mane when you have to plait up, it depends if your horse is in medium competition work then a blanket clip would be the way to go I think. That's what I have on Jaffa
Most places recommend pulling manes after a harder/hot workout while breaking it up into a few separate sessions. Clipping blades all depend on the desired length of fur. Our show horses get a 10-20 depending on color and coat texture!